RN3200 XRAID Expansion - Sanity Check.

onestopit wrote:

Folks, We have an existing 6TB (6 x 1TB Factory Stock Drives) in a XRAID2 array which we are looking to expand with the addition of 3 x 2Tb drives from the approved drive list. Ideally I would like to perform an online expansion but also looking for speed of expansion across the additional drives. Would I be better doing this drive by drive online, or shutting down - inserting the new drives and restarting so all drives are included at same time?

Optional - First I would schedule some downtime for several hours and run the "Disk Test" boot option: http://www.readynas.com/kb/faq/boot/how_do_i_use_the_boot_menu

This will help flag if one of your disks already in the NAS is failing/dead. The long offline SMART tests are very thorough. The short online daily SMART tests are relatively fast involve some randomness and are more likely to miss a failing disk. Whilst this should be fine in day to day usage, when adding a disk to your volume you put heavy stress on all disks, so it's best to remove dead/failing disks before adding additional ones.

I would add one drive at a time online, wait for resync to complete then add next disk.
Under Volume > Volume Settings, does your volume show as X-RAID2 dual-redundancy or just X-RAID2? I would expect it would probably show as X-RAID2 dual-redundancy

onestopit wrote:
Also, if we insert the additional 3 x 2Tb drives do we just get 3Tb additional space or 4Tb? ie: Do they get viewed as 1Tb drives along with the other existing 1Tb drives or do they get viewed as 2Tb drives and therefore once 2nd/3rd drive is inserted this then becomes 4/6Tb additional space depending on how drives are striped into existing array?

Assuming you are using the default X-RAID2 dual-redundancy they will be seen as 1TB disks. If you added a fourth 2TB disk you would have the horizontal expansion of an additional 1TB and then the vertical expansion to use additional redundant space.

Take a look at 6-bay dual-redundancy example expansion paths

Whilst written for 6-bay units the principles are the same with 12 bay units.

Thanks for the quick reply. So... to clarify... if I have 6Tb (6 x 1Tb) in XRAID-2 I have 4Tb usuable, then I add three 2Tb drives into the equation in slots 7/8/9 I would then gain 3Tb (as all drives seen as 1Tb until a fourth drive inserted)... but if I had a fourth drive in slot 10 I would then also benefit from vertical expansion - but would this give me another 2Tb, 3Tb or 4Tb?

O.K. you have 6x1TB with 4TB usable. Add 3x2TB disks giving you an additional 3TB usable (horizontal expansion). Add a further 2TB disk this gives you an additional 1TB horizontal expansion. Then on top of this there is vertical expansion, with a new RAID-6 layer of 4x1TB giving 2TB of vertical expansion. Remember expansion can only take place when redundant space can be added.

So 4TB + 3TB + 1TB + 2TB = 10TB. This is of course before discrepancies in measurement and overheads etc.

the 3200 uses dual redundancy by default, so unless single redundancy was manually chosen, the vertical expansion will result in ~2tb additional.

2 raid layers;
6x 1tb + 4x1tb (from 2tb drives) minus 2x 1tb for dual redundancy (~8tb)
4x 1tb (from the 2tb drives) minus 2x 1tb for dual redundancy (~2tb)
= ~10tb gross, net usable is gonna be about 9 to 9.5tb.

Perfect.. thanks for the feedback. Can you also confirm if what I read about plugging in all new drives at once during a powerdown and powering up again will automatically expand over these disks (rather than doing one by one online) is 1. possible, and 2. a good idea?

It's possible. The disks will still be added one at a time though. My preference would be to hot-add (add while NAS is on) one disk at a time.

This unit is located in CoLo, so depending on time taken to do each drive in turn whilst "hot" might be a pain so doing it in such as way to plug all the drives in one go and leaving it to sort itself out might still be the way I'll go... unless somebody out there yells "DON'T DO IT!!!" - with a valid reason too. :D

Would the storage be available whilst all the drives are done in one pass, or would it appear offline? Are there any performance gains between one a go and four a go methods?

putting them in individually is the safest way, this will help protect from drives that die early.

if you put all 4 in and powered up, then 3 of the new drives failed, you could lose the whole array.

putting one drive in a time, you suffere only 1 drive failure (well unless the failure happens from one or more of the older existing drives).

In any case, its important to always have a current backup of all data before making large changes such as adding a bunch of drives.